netdev - Re: [PATCH 2/3] ARM: Select ARCH_USES_CFI_GENERIC_LLVM

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Message-ID: <CACRpkdaeOYEcK9w1oy59WBqjNrK7q5zT2rzg8pHgDdZdKWVKZg@mail.gmail.com>
Date: Mon, 27 Oct 2025 23:56:21 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Nathan Chancellor <nathan@...nel.org>, Kees Cook <kees@...nel.org>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Russell King <linux@...linux.org.uk>, Tony Nguyen <anthony.l.nguyen@...el.com>, 
	Michal Kubiak <michal.kubiak@...el.com>, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH 2/3] ARM: Select ARCH_USES_CFI_GENERIC_LLVM_PASS

On Mon, Oct 27, 2025 at 4:54 PM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> On Sat, Oct 25, 2025 at 1:53 PM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > Prior to clang 22.0.0 [1], ARM did not have an architecture specific
> > kCFI bundle lowering in the backend, which may cause issues. Select
> > CONFIG_ARCH_USES_CFI_GENERIC_LLVM_PASS to enable use of __nocfi_generic.
> >
> > Link: https://github.com/llvm/llvm-project/commit/d130f402642fba3d065aacb506cb061c899558de [1]
> > Link: https://github.com/ClangBuiltLinux/linux/issues/2124
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>

I didn't know Kees stepped in and fixed this, christmas comes
early this year! I had it on my TODO to do this or get someone to
do this, but now it turns out I don't have to.

> > +       # https://github.com/llvm/llvm-project/commit/d130f402642fba3d065aacb506cb061c899558de
> > +       select ARCH_USES_CFI_GENERIC_LLVM_PASS if CLANG_VERSION < 220000
>
> Instead of working around issues with the generic pass, would it make
> more sense to just disable arm32 CFI with older Clang versions
> entirely? Linus, any thoughts?

We have people using this with the default compilers that come with
Debiand and Fedora. I would say as soon as the latest release of
the major distributions supports this, we can drop support for older
compilers.

Yours,
Linus Walleij